In What Order Index Sorts The Data???
Sep 20, 2007
Hi,
I want to ask a basic question, that is
IN WHAT ORDER A CLUSTERED INDEX SORT THE DATA IN THE COLUMN????
Somewhere in the MSDN library I read the following line:
"A clustered index physically sorts the table's contents in the order of the specified index columns"
But Sorting means it will be in ASCENDING ORDER (ASC) or It will be in DESCENDING ORDER (DESC)
So my question is lets suppose a column on which the cluistered index is defined and it contains character data liek abcd so in wht order it will sort the data alphabetically ASC or DESC
or
If the same above case with integer type of values, if column having integer values then in wht order the data in the table will be sorted.
??????
Thanks..!!!
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Mar 26, 2007
Hi
I was going through the book by Kalen Delaney where she has mentioned the following paragpraph in Chapter 7 (Index Internals):
Many documents describing SQL Server indexes will tell you that the clustered index physically stores the data in sorted order. This can be misleading if you think of physical storage as the disk itself. If a clustered index had to keep the data on the actual disk in a particular order, it could be prohibitively expensive to make changes. If a page got too full and had to be split in two, all the data on all the succeeding pages would have to be moved down. Sorted order in a clustered index simply means that the data page chain is logically in order.
Then I read the book on SQL Server 2000 (on Perf Tuning) by Ken England. He says the clustered index stores data in physical order and any insert means moving the data physically. Also the same statement is echoed on the net by many articles.
What is the truth? How are really clustered index stored? What does physical order in the above statement really mean?
Regards
SanjaySi
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Apr 15, 2015
We are running SQL Server 2014 Enterprise Edition (64-Bit) on Windows 2012 R2 Standard (64-Bit).
1. When to create indexes, before or after data is added? Please address Clustered and Non-Clustered Indexes.
2. To move indexes to it's own filegroup, is it best to create the NON-Clustered Indexes on the separate filegroup with code similar to the example below?
CREATE NONCLUSTERED INDEX IX_Employee_OrganizationLevel_OrganizationNode
ON HumanResources.Employee (OrganizationLevel, OrganizationNode)
WITH (DROP_EXISTING = ON)
ON TransactionsFG1;
GO
I have read the following links that states that if you create the Clustered Index on a separate filegroup, it would also move the base table to that particular filegroup. (So I take it that you ONLY can move NON-CLustered Indexes to a separate filegroup.)
Placing Indexes on Filegroups:
[URL]
By default, indexes are stored in the same filegroup as the base table on which the index is created. A nonpartitioned clustered index and the base table always reside in the same filegroup. However, you can do the following:
• Create nonclustered indexes on a filegroup other than the filegroup of the base table.
Move an Existing Index to a Different Filegroup:
[URL]
Limitations and Restrictions
• If a table has a clustered index, moving the clustered index to a new filegroup moves the table to that filegroup.
• You cannot move indexes created using a UNIQUE or PRIMARY KEY constraint using Management Studio. To move these indexes use the CREATE INDEX statement with the (DROP_EXISTING=ON) option in Transact-SQL.
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Mar 5, 2015
I have a clustered index that consists of 3 int columns in this order: DateKey, LocationKey, ItemKey (there are many other columns in this data warehouse table such as quantities, prices, etc.).
Now I want to add a non-clustered index on just one of the other columns, say LocationKey, like this:
CREATE INDEX IX_test on TableName (LocationKey)
I understand that the clustered index keys will also be added as key columns to any NC indexes. So, in this case the NC index will also get the other two columns from the clustered index added as key columns. But, in what order will they be added?
Will the resulting index keys on this new NC index effectively be:
LocationKey, DateKey, ItemKey
OR
LocationKey, ItemKey, DateKey
Do the clustering keys get added to a NC index in the same order as they are defined in the clustered index?
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Nov 27, 2007
I have a fact table with SalesAmount. I have a dimension with SalesType - either counter or direct.
I want to display a report that shows direct sales by region. No problem. I group on region and filter by direct sales.
However, I also want to show direct sales as a percentage of total sales. I've played around with multiple tables but I can't seem to find a way to display both direct sales and total sales in the same row of a report.
Any suggestions?
Thanks.
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Jun 19, 2013
I want to make an index with the following columns, actually together they constitute the PK of the table so the index is created automatically.
The question is witch sort order is the best to have if I want to fetch all rows for one date and one resource? And why?
WHERE Resource = "Car 1" AND Date = "2013-03-03"
Resource, Date, Time
Or
Date, Time, Resource
Below is an example with tree resources, but in reality there can be a lot more and also years of dates.
Car 1, 2013-03-03, 10.00
Car 1, 2013-03-03, 11.00
Car 1, 2013-03-03, 12.00
Car 1, 2013-03-04, 10.00
[Code] ......
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May 20, 2008
Is there a dynamic management view or system procedure which I can use to find out what columns are in an index, what columns are as an INCLUDE in the index and whether or not the column(s) are ascending or descending. This is excluding the utilities I already know about below:
sys.indexes
sys.index_columns
sp_helpindex
dm_db_index_physical_stats
dm_db_index_operational_stats
I only ask because it is a pain to look through the sys.indexes and sys.index_columns tables every time I want to know about what columns are in the index created. I also know that scripting the index would give me the information I need but there must be a better way.
Many Thanks
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Aug 23, 2007
I wrote some views in sql2000 and all was well. I upgraded to sql 2005 and non of the order by clauses work when I run the views directly. If I open the view up in desing mode and run them, they work.
Any Ideas?
Thanks,
Rick
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May 16, 2007
Hi,
When I execute the following statement:
Select * from table1;
On what basis, SQL server decides the sequence of these rows?
I need to fetch data from a table with very large number of rows. Because of the datasize I need to do this in chunks. I am thinking of passing row counter and fetch N rows at a time. I want to know if there is a need for sorting a table before I apply the above logic or I can rely on default sorting.
Thanks veyr much.
Regards,
Tim
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Apr 7, 2008
Recently I was stumped on a problem where I was granting permissions to a user, from within a script that was creating a stored procedure. Then I would check the permissions on the procedure, but the permissions were empty. It turned out that I was missing a "go" statement to seperate the create procedure statement from the grant statement. So that got me to thinking about what other kids of statements must be seperated into seperate batches ? I would thik that anything that is being created must be seperated from any statements that grant or alter permissions, because the items would need to exist first.
comments ?
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Apr 15, 2003
Does anyone have a general rule or guide on when to use this SQL 2000 option when creating indexes? I was thinking generally on nonclustered indexes where the column would be unique and incremental and usually filtered on by range and often used in the order by clause. Such as columns of datetime or integers datatypes. Thanks.
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Feb 29, 2008
I have a table "Client" that has two columns: "ClientID" and "ProductID". I created on clustered index on ClientID and when I opened the table in the management studio, I saw the table was in the order of ClientID.
Then I added another non-clustered index on ProductID. When I open the table again, it is in the order of ProductID. Shouldn't the table always be in the order of clustered index? Non-clustered index should be a structure outside of the table itself? Did I do anything wrong?
Thanks for any hint.
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Jun 9, 2006
Hi,I created a composite index (lastname, firstname). I know the followingqueries will use this index:WHERE lastname = ...WHERE lastname = ... AND firstname = ...Also this won't use the index:WHERE firstname = ...But how about: WHERE firstname = .. AND lastname = ...And why?Thanks a lot,Baihao--Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
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Jul 20, 2005
Hi allI recently noticed when trying to optimise a major query of a chess websiteI am the webmaster of, that adding an order by for "gamenumber" which is aclustered index field as in for example "order by timeleft desc, gamenumberdesc" actually speeded up the queries and reduced sql server 2000 timeouts.I have an ASP error log and I am fairly sure that a dramatic reduction insql server timeouts is simply attributed to adding an extra seeminglyredundant order by field - which is the clustered index. Is this phenomenaat all possible or is it my imagination?!Other special attributes of the query includes the use of "Top" to obtain amaximum specified number of rows. Perhaps it is just the uniquecharacteristics of the query, but I would have thought that the less orderby fields would imply faster performance. Has anyone else noticed that aseemingly redundant order by column on for example the clustered indexcolumn, can actually help speed up queries?!Best wishesTryfon GavrielWebmasterwww.chessworld.net
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May 29, 2007
I have 2 columns in a table namely ColA and ColB.all DML operations are through views n every view has
Where clause i.e where ColA=€?€? with check option .
All most all my DML queries are using where clause on ColB
Where ColB=€?€?
Now my question is I have a clusted index on both ColA and ColB.in which order I have to create cluster index .
i.e ColA ASC,ColB ASC or ColB ASC,ColA ASC.
Is there any performance gain we can achieve with their order
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Aug 22, 2007
We are using partitioned unique indexes on partitioned tables. When the Unique Index is built, should the column the index is partitioned by be the top (leftmost) column in the index? While this violates cardinality, it makes sense (at least to me) that the first thing the query execution would do is figure out which partition(s) contain the result set, then filter from there.
What do you guys think? Is there any documentation on optimizing partitioned indexes?
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May 19, 2015
I never paid much attention to this before but I noticed this today in a new table I was creating.
For tables defined in the tabular model the table properties have something like SELECT Blah FROM TableName ORDER BY Blah Then in the tabular model the table's data is in the same order it was ordered by in the data source for the table.
I have a date table I setup and I noticed it is NOT respecting the sort order.
I have it sorted by DateID which sorts with the oldest date first and newest date as last row.However, the table that is imported and stored in the data model is not in that order.
I can of course manually sort the rows in BIDS/DataTools, but I find this discrepancy odd.
Would this have negative impacts on the EARLIER function for example if the data rows are not in the order specified?
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May 29, 2007
Want to check my thinking with you folks...
I have a table with a clustered composite index, consisting of 3 columns, which together form a unique key. For illustration, the columns are C1, C2 & C3.
Counts of distinct values for columns are C1 425, C2 300,000 & C3 4,000,000
C3 is effectively number of seconds since 01/01/1970.
The usage of the table is typically, insert a row, do something else, then update it.
Currently, the index columns are ordered C3,C1,C2. Fill factor of 90%.
My thinking is that this composite index is better ordered C1,C2,C3.
My reasoning is that having C3 as the leading column, biases all the inserts towards one side of the indexes underlying B-tree, causing page splits. Also, there'll be a bunch of "wasted" space across the tree, as the values going into C3 only ever get bigger (like an identity), so the space due to the fill factor in lower values never gets used.
Welcome your thoughts.
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Dec 28, 2005
Hi all,
I'm getting this "invalid descriptor index" exception while trying to fetch a record from the table.
The query is "select * from <tablename> where <columnname> = 'xyz'". The column name is correct and indeed a record with 'xyz' value exists. The record is getting fetched too...! But I'm having this particular error while trying to retrieve a couple of fields with rs.getString().
The order of columns in the table is same as the order in which I'm retrieving them. And I'm not facing any problem retrieving another field which has width of 200 characters.
I'll be very grateful indeed if someone can help me out of this particular problem...
Cheers, mates!
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Jun 11, 2007
I upsized an access database with a key / index on ordernumber and linenumber.
However if I open the table in the Management Studio the records aren't ordered this way (same goes for select * from table) I get:
Ordernumber
Linenumber
200724001
37
200724004
3
200724006
33
200724001
3
200724011
19
200724014
5
200724006
37
200724011
19
200724006
28
Same goes for my crystal reports files, since the records aren't ordered by ordernumber / linenumber all my formulas go bezerk..
Am I wrong thinking the records should be ordered according to the prim. index?
Please help because I don't want to have to change all my 40+ reports to include an "ORDER BY"
Best regards,
Mike
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Sep 16, 2015
In SQL 2012.A query that joins 2 table, with order by clause doesn't get sorted and the result set is not ordered. This happens when some of the columns in the where criteria are in a unique index which is the index that is used for the join between the 2 tables, and all the columns in the unique index are in the where criteria.In the query plan there is no component for sort.The work around was to drop the unique index, or change it to a non-unique index. Once this was done, the execution plan was changed to add the sort component (even when the index was changed to non-unique and the join was still using this index).
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Sep 5, 2015
I am really puzzled by an apparent difference between table index key column order and its statistics order. I was under understanding that index statistics mirror index definition. However, in my db 2470 index ordinal definitions match statistics definition but 66 do not. I also can reproduce such discrepancy in 2008 R2, 2012 and 2014.
As per definition,
stats_column_id
int
1-based ordinal within set of stats columns
This script duplicates this for me.
BEGIN TRAN
GO
use tempdb
GO
CREATE TABLE [dbo].[ItemProperties](
[itmID] [int] NOT NULL,
[cpID] [smallint] NOT NULL,
[ipuID] [tinyint] NOT NULL,
[Code] ....
The result I get is this:
object_id      stats_name                                    Â
stats_column_list
1525580473 PK_ItemProperties_itmID_ipuID_cpID itmID, cpID, ipuID,
and
object_id      index_name                                    Â
index_column_list
1525580473 PK_ItemProperties_itmID_ipuID_cpID itmID, ipuID, cpID,
Also a query I used to discover this in my db is:
WITH stat AS
(
SELECT
s.object_id
,s.name as stats_name
,(
SELECT
c.name + ', ' as [data()]
FROM sys.stats_columns as sc
[Code] .....
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Feb 24, 2007
I am using the following query to export data from sql server to ms access in export data wizard:
SELECT * FROM myView where myID = 123
Order by varcharColumnName1,varcharColumnName2 ,intColumnName3
This query will fetch about 7, 00,000 records.
SQL server 2005 shows the correct order, but Data in access table shows Incorrect data.
Please give me the solutions.
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Oct 20, 2006
please explain the differences btween this logical & phisicall operations that we can see therir graphical icons in execution plan tab in Management Studio
thank you in advance
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Apr 9, 2007
Hello All,I have a SQLDataSource "sdsX" which has four records. There is a DataList "dlX" which is binded to this SQLDataSource "sdsX". Now I want that my datalist "dlX" take third record of "sdsX" as its first element. Is there any property which can be used.Thanks
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Dec 7, 2007
Title is probably poorly worded
Say I have a table setup like this:
Code:
AccountID | GeneratedDesc | Col1 | Col2 | Col3 | Order
-------------------------------------------
1|| Data1 | Data2 | Data3 | 1,2,3
2|| Data1 | Data2 | Data3 | 1,3,2
3|| Data1 | Data2 | Data3 | 2,3,1
1|| Data1 | Data2 | Data3 | 1,2,3
Basically, I want to set GeneratedDesc = Data1 + ' ' + Data2 + ' ' + Data3 where an account sets the order 1,2,3
GeneratedDesc = Data2 + ' ' + Data3 + ' ' + Data1 where an account sets the order 2,3,1
Basically, The Generated Description is set in an order that is chosen by the Account.
I am not sure how to go about doing this, outside of dynamically generating the query and looping throughout all the rows in the table, which, i think for large amounts of data, can get expensive. I don't think creating a query for each combination would be good either (in this case, 6 combinations, but for larger order sets, such as 6, can get quite alot of queries).
any ideas? (not sure if this makes sense to anyone)
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Jan 8, 2008
This is related to SQL Server 2005
I have a table named BranchDetails having a column named branchnumber.
The data in the branch is in the following order
2007-90
2006-9
2007-67
2006-8
2007-98
2007-56
2006-1
Null
I want to write a T SQL query that will bring the result in the following descending order
with null at the top
Null
2007-98
2007-90
2007-67
2007-56
2006-9
2006-8
2006-1
Can someone show me the T sql statement?
Thanks.
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Nov 9, 2007
i have a table Animals with column names id and Name eg1 Tiger2 Lion3 Elephant4 Cheetah5 Zebra i want the order to be anything of my chossing when i select from it. eg how could i get it to display results in this order (when i do select * from Animals): CheetahElephantZebraTiger Lion Thanks
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Aug 16, 2002
Hi ,
Hopw can i sort the data in the ascending order so that i can see the date of my log files imported at the top of my table .
Right now my log files get imported and appended in the tables but they get appended in the descending order at the bottom of the last data .
Is there any way to sort the data so that i can see it in the reverse way when i open my tables ?
Many Thanks .
Anita.
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Feb 10, 2015
This query works perfectly and orders by just as I need
Code:
Select
'1st' As [Type],
#Uno.ID
#Uno.Address,
#Uno.shippingInfo
FROM #Uno
[Code] ....
However, when I use it in a Union All so I can pull data from 2 diff tables, the order by statement no longer works. How can I order by data in 2 tables?
Code:
Select
'1st' As [Type],
#Uno.ID
#Uno.Address,
#Uno.shippingInfo
FROM #Uno
[Code] ....
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Mar 7, 2013
When We sort the data by using ORDER BY , which sorting algorithm method will be used by SQL optimizer?
1) Bubble Sort
2) Quick Sort
3) Merge Sort
4) Heap Sort
5) Insertion Sort
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Apr 16, 2008
Hi,
Is there a preferred backup order for backing up data and log files?
Which is preferable to backup first?
Thank you,
Seb.
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Jan 8, 2008
Hi
I have a table with column name starts from col1 to col20. IS their anyway to insert the data and sort the table by col1 and col2 and SAVE IT.
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